The invention is directed to a shielding container for the transportation and/or storage of spent fuel elements having a neutron shield on the outer surface of the container.
Containers which are employed for the transportation and/or storage of spent fuel elements must safely seal in the radioactivity of the inserted material and in rigorous tests demonstrate that this is guaranteed even in extreme disaster situations. However, simultaneously they must also shield off the gamma and neutron rays set free in the radioactive decay reactions and carry off the decay heat to the outside.
Known shielding containers for the most part consist of a metallic base container with the necessary wall thickness for shielding the gamma rays, customarily of steel or a combination of lead and steel and an outer shell of neutron shielding material, for the most part polyethylene pellets filled in synthetic resin. Normally there are welded or soldered on the metallic base flanges or fins which penetrate the resin layer. They are necessary to increase the metallic surface of containers which are laid out for a high heat conductivity and for carrying off the heat through the in general poor heat conducting neutron shielding layer.
The disadvantage of this construction is that slight collisions of the containers, as can occur even in routine operation can lead to damage to the heat conducting fins and the resin layer and accordingly make necessary an expensive repair of the entire container.
Furthermore, it is scarcely possible to carry out a cleansing or, in the case of contamination, a decontamination, of the outer surface of the container built of fins or flanges. This must therefore be protected through applying a protective shell in the handling operations in which there is the danger of a contaimination of the surface, thus for example in the loading and unloading.
A further disadvantage of this known shielding container is that the number of heat conducting fins and the thickness of the neutron shield must be designed for the maximum predicted conditions in transportation. However, in a great part of transportation containers and storage containers spent fuel elements are included which are already so far decayed in the fuel element storage tanks of the nuclear power plant that in the cases both the neutron shielding and the fin surfaces of the container are oversized.
Therefore it was the problem of the present invention to provide a shielding container for the transportation and/or storage of spent fuel elements with a neutron shield on the outer container surface in which it is possible to make a repair on the neutron shield without repairing the entire container, in which manipulative operations are possible without danger of contamination as well as without applying a protective shell and which in a given case can be adjusted to the changing requirements of the individual case with reference to irradiation intensity.